'Truth spoken without moderation reverses itself'
This blog is a source for intellectual exploration. It includes a list of alternative resources and a source of free books. The placement of an article does not imply that I agree with it, merely that I found it thought-provoking. There are also poems and book reviews. Texts written by me are labelled. Readers are free to re-post anything they like.

Saturday, March 4, 2017

Nicola Davis - Do the Quebec fossils prove that life begin much earlier than we thought?

A team of scientists
say they have discovered the oldest
fossils on Earth in rocks from Quebec. Dating techniques suggest the
rocks are at least 3.8bn years old, and might even be 4.3bn years old.

What do these
fossils look like?They are tiny. They consist of
filaments and tubes up to half a millimetre in length and around half the width
of a human hair. They’re made of haematite, a type of iron oxide (better known
as rust). Some of the filaments resemble loose coils, some are branched, and
others appear to be joined to knobs of haematite. The tubes and filaments are
thought to be the remains of bacteria that lived on iron and dwelt around
hydrothermal vent systems – mineral-rich hot springs – on the seafloor. Similar
systems have been
proposed as a likely location for where life first arose.

How do we know the
bacteria lived underwater?Telltale chemical signatures,
and distinctive structures such as pillow-shaped masses, point to an underwater
formation for the rocks. The fossils themselves were discovered in a type of
iron-rich quartz known as jasper. This jasper was found between volcanic rocks,
and probably formed as material ejected from hydrothermal vents settled.

How do we know
these tubes and filaments are fossils?That’s the tricky bit. The
authors of the study say they are confident for several reasons. They argue
that the haematite structures are similar to those produced by iron-oxidising
bacteria today, as well as to microfossils found in younger rocks, hundreds of
millions – rather than billions – of years old. What’s more, the structures
were found to contain graphite as well as the minerals apatite and carbonate –
which are associated with biological matter. Finally, the team found iron-oxide
granules and, in other sections of the rocks, structures such as carbonate
rosettes (also associated with apatite, graphite and carbonate), which, they
say, could have formed as biological matter broke down.

Does everyone
agree?No. While the researchers say
their investigation ruled out the chance that the structures were formed by
geological processes, others are not convinced. The rocks in which the fossils
were found are metamorphic, meaning that they have experienced high
temperatures and pressures since they formed – some argue that this could have
produced the structures instead. The size and arrangement of the haematite
structures has also raised concerns, as has the fact that the microbes would
have relied on oxygen at a time oxygen is thought to have been scarce. .

How does this fit
in with other ancient fossil finds?The previous “oldest fossils”
date to about 3.5bn years ago and were found in Western Australia. However,
they have been the subject of hot debate, with many experts unconvinced they
are the remains of microbes. Another finding was reported last year, with
researchers claiming that they had found fossil traces of microbial activity,
known as stromatolites, in rocks
from Greenland dating to 3.7bn years ago – 220m years older than the
previous oldest known stromatolites. Again, experts were split on whether the
evidence was strong enough to suggest the structures were made by organisms,
rather than through geological processes. Other younger and better-preserved finds
are less contentious.

What does this tell
us about early life on Earth?If the structures are
microfossils, the discovery shows that fairly sophisticated microbes might have
been around as early as 4.3bn years ago, pushing back the origins of life on
Earth to, potentially, 4.4bn years ago. With planet Earth only 4.5bn years old,
that suggests life got going and diversified pretty quickly. That raises the
possibility that life can crop up rapidly when the right conditions are
present.

What does this mean
for the search for life “out there”?We know that, in its early
beginnings, Mars, like Earth, had oceans. If these newly discovered structures
are fossils, it raises the possibility that microbes were also thriving on Mars
– and offers clues as to what scientists should be looking for in rocks on the
red planet. The find also supports the idea that other bodies in the solar
system, such as Jupiter’s moon Europa, might be good places to look for life,
since it has been proposed that Europa might have hydrothermal vents under its
icy shell.